What's the Radiation Exposure to Animals after Owner's Radioiodine Treatment?

I am suffering from hyperthyroid due to Graves' disease, and I'm being treated with radioactive iodine next week.

My doctor says that I will be able to go right home after my treatment, but that I shouldn't sleep with my husband for at least 5 days.  I don't have any children, but I do have my two male cats, aged 3 and 6 years.  I asked my doctor about my cat's exposure, but he didn't seem to know (or care).

Is there any problem with me being around my cats after I get treated? Can I make my cats (or husband) radioactive? If so, what precautions should I take so that doesn't happen.

My Response:
This is a common question that I get. Once you are treated with radioiodine and return home to your husband and cats, they are all going to be exposed to the gamma radiation emitted by you for a period of 2-3 weeks or so, depending on the dose of I-131 administered.

Although it highly unlikely that this radiation exposure would do harm to your family members, we want to minimize the amount of exposure to as low as reasonably possible. If this radiation exposure was certain to cause harm or damage, I would certainly be in deep trouble. Remember that I have been exposed to the radiation emitted from my hyperthyroid cats for the 32 years that I have treating them with radioiodine, and I still feel fine!

Radiation safety recommendations
To minimize the gamma radiation exposure to your cats, I would treat them exactly like I would treat any other member of the family (1-4). To that end, I recommend that you follow the American Thyroid Association's guidelines and take the following steps to help reduce the radiation exposure to your cats (and husband) after your treatment:

• Sleep in a separate bed for at least 1 week (2 weeks is better), especially if your cats sleep within 3-6 feet of your body.
• Maintain a distance of a least a 3-6 feet from your cats as much as possible.
• It's fine to pet your cats, but limit close contact (closer than 3 feet) to less than 30 minutes a day.
• Do not prepare their food, since you could potentially contaminate what they eat (same goes for your husband).

The length of time needed to continue these precautions will depend upon the dose administered, so you should talk to your physician about what he recommends for your husband, and then I'd follow the same rules for your cats.

For more information about Radiation Safety Recommendations, check out the information about radioiodine and how to reduce exposure after I-131 treatment on the American Thyroid Association website.

Can you make your cats radioactive?
The short answer is — no, you cannot make your cats radioactive unless they ingest food that you have contaminated. I would have your husband feed your cats, or if that isn't possible, you should wear gloves when preparing their food.

When you are close to your cats or your husband, you will be exposing them to the radioactive emissions coming from your body. These emissions are gamma rays, one of the types of electromagnetic radiation, and are similar to x-rays. All electromagnetic radiation travels at the speed of light (or approximately 300,000,000 meters per second), so your cats will not be able to outrun this radiation.

Fortunately, if you step back from your cats, these gamma rays will not be very strong and they will not reach your cats. Even if your cats are too close to you and are exposed to your emmissions, they will NOT retain the radiative waves that they received by being close to you  — again, once you step away, the gamma rays continue traveling at the speed of light until they dissipate.

It's like going to the beach on a nice sunny day. We receive radiation exposure from the sunlight that hits our exposed body during the day, but as soon as the sun goes down, we stop receiving radiation exposure. In this case, you, as the patient treated with the radioiodine, are acting like the "sun." We don't become radioactive or excrete radiation after spending a day at the beach, and neither will your cats after being close to you for a few minutes each day.

References:

1. Zanzonico PB. Radiation dose to patients and relatives incident to 131I therapy. Thyroid 1997;7:199-204.  
2. Marriott CJ, Webber CE, Gulenchyn KY. Radiation exposure for 'caregivers' during high-dose outpatient radioiodine therapy. Radiat Prot Dosimetry 2007;123:62-67.  
3. Sisson JC, Freitas J, McDougall IR, et al. Radiation safety in the treatment of patients with thyroid diseases by radioiodine 131-I: Practice recommendations of the American Thyroid Association. Thyroid 2011;21:335-346.  
4. American Thyroid Association (ATA) website. Radioiodine. 

Update on the Perilous Situation of Dogs & Cat Exposed to Radiation Fallout from the Fukushima Nuclear Disaster

Thousands of dogs and cats were abandoned after an earthquake damaged Japan's Fukushima nuclear plant, and continued radiation concerns have stymied recovery efforts.

Although the radioactive material the dogs and cats were exposed to during the disaster should be cleared by the their bodies by now, the animals may have incurred permanent damage according to Timothy Mousseau, a professor of biological sciences at the University of South Carolina, who has extensively studied animals exposed to radiation.

Mousseau's research has found significant genetic damage and breakages in chromosomes among animals exposed to radiation in and around Chernobyl, a situation similar to that of Fukushima. Developmental abnormalities, tumors, and species decline and extinction have also been attributed to radiation exposure in that area, and are likely to also occur in Japan.

To read the story and see photos of dogs and cats living near the Fukushima nuclear plant, which was published in PBS Newshour, the Rundown Blog, click this link.

For an overall update on the situation in Japan, click this link to view a podcast more about the persistent radiation readings around the Fukushima area on the PBS Newshour website.

Checking Colleague Just Back From Japan For Radiation Contamination

This week, one of my veterinary colleagues returned from a 3-week visit to Japan. She was obviously worried about possible radiation exposure in the aftermath of the Japan nuclear crisis and asked for my advice about how she could check for radiation contamination.

I asked her to come to my office today so that I could monitor her for any radiation contamination.  I have the radiation instruments in both of my offices because we routinely treat hyperthyroid cats with radioactive iodine (I-131). (See my website for more information.)  My staff and I use this radiation detection equipment on a daily basis in order to check for contamination, both on our bodies and well as in our work environment (this is a safety precaution - we do NOT expect or plan on becoming contaminated!).

I first monitored my colleague by use of a general purpose survey meter (Geiger counter). With this meter, I've attached a GM (geiger-mueller) pancake detector, which is sensitive to alpha, beta and gamma radiation and is the industry standard for detecting contamination.

Fortunately, I found absolutely no detectable levels of external contamination with my measurements.

Dr. Peterson checking for external radiation contamination

We next measured my colleague's thyroid gland for internal contamination. As you may know, the principal radiation source of concern with the nuclear reactor accident in Japan is the release of radioactive iodine (I-131). This radioactive isotope that presents a special risk to health because iodine is normally concentrated in the thyroid gland. Exposure of the thyroid to high levels of radioactive iodine may lead to development of thyroid nodules and thyroid cancer years later. 

Counting thyroid gland for I-131 contamination

To measure for internal (thyroid) contamination of I-131, we used a general purpose radiation scaler/ratemeter attached to a shielded well gamma radiation counter. This is a very sensitive instrument, which allows us to detect very tiny amounts of gamma radiation, including the gamma rays (photons) emitted from I-131.

Radiation counts below background readings, indicating no contamination

Fortunately, the thyroid counts measured in my colleague (373 counts per minute or cpm) were below the background radiation counts of 385 cpm. This demonstrated that there was NO internal thyroid radiation.

Overall, we found NO external or internal contamination in my colleague. All good news!  

The fact that we measured a background radiation count is a normal, expected finding: background radiation is constantly present in the environment and is emitted from a variety of natural and artificial sources. See this article for more information on background radiation.

Radiation Toxicity, Potassium Iodide, and Our Pets

Over the past week I have received a number of questions about radiation both from pet owners and veterinarians about the danger from the nuclear fallout from Japan, not for their human families but also for their dogs and cats.

The question is: should we all be buying potassium iodide for ourselves? Should we also give this to our pets? Since dogs and cats are smaller than we are, could they be impacted by smaller amounts of radiation? What should we do?

The answer to these questions, at least for the time being, is not to take potassium iodide or administer the drug to our pets. So far, the amount of radiation coming here from Japan has been termed negligible by our government. 

What's more, potassium iodide only helps pets (or people) to deal with radioactive particles (I-131) which ultimately impact the thyroid gland, not other organs or illnesses which may result from excessive exposure to radiation.  I understand that we care about our pets and want to be proactive, but we might do more harm than good by giving this iodide supplement.

How does potassium iodine work?

The thyroid gland is the only tissue in the body that wants or needs iodine to perform its normal function (i.e., to make the thyroid hormones T4 and T3, both of which contain iodine in their hormone structure).  As you can see, in the figure on the right, thyroxine or T4 (the main thyroid hormone secreted by the thyroid gland), contains 4 iodine groups on the hormone molecule. T3, the other main thyroid hormone, contains 3 iodine groups on the molecule.

By saturating the thyroid with stable iodide (i.e., non-radioactive iodine), potassium iodide works to block the effects of radioiodine (I-131) on the thyroid gland. In other words, if your thyroid already has all the iodine it needs it will refuse to take up the  I-131.

Of course, there's a catch. Doses of potassium iodide high enough to protect your thyroid from I-131 have some nasty side effects. 

What are the adverse effects of potassium iodide?

Side effects associated with administration of potassium iodide may include gastrointestinal upset, allergic reactions, skin rashes, salivary gland inflammation, hyperthyroidism, or hypothyroidism. That is a pretty impressive list of side effects!

So what should we do?
Since radioactive iodine (I-131) decays rapidly, current estimates indicate there will not be a hazardous level of radiation reaching the United States from this accident. If and when an exposure does warrant the use of potassium iodide, it should be taken as directed by physicians or public health authorities until the risk for significant exposure to radioactive iodine dissipates, but probably for no more than 1 to 2 weeks.

Again, unless the experts declare that radiation levels are high enough, we shouldn't take it or administer it to our pets. If you're determined to purchase potassium iodide for you or your pet, please beware —many legitimate outlets are sold out, particularly if you purchase the potassium iodide online.